%%% Surrounded math
\newcount\repeater
\def\dorecurse#1#2{% just a helper
\repeater=0 \loop
#2%
\advance\repeater by1
\ifnum\repeater<#1\relax
\repeat}
\def\CONTEXT{Con\TeX{}t}
One of those features that the average user will never see is the ability to
influence \type {\mathsurround}. In \CONTEXT\ for instance this parameter is
set to \type {0pt} by default and only in special math constructs it might get
a different value. And even then, this value is small.
It might actually be true that the sole reason for this parameter is its use in
special situations. This is demonstrated by what happens if we use non-zero
values. Say that we have this input:
\beginverbatim
test \par
\noindent $test$ \par
$test$ \par
test \par
\endverbatim
\def\test{%
test \par
\noindent $test$ \par
$test$ \par
test \par
}
When we set both \type {\parindent} and \type {\mathsurround} to zero, we get:
{\mathsurround 0pt \parindent 0pt \test }
When we set \type {\mathsurround} to \type {16pt} we get:
{\mathsurround 16pt \parindent 0pt \test }
When we set \type {\parindent} to \type {32pt} we get:
{\mathsurround 0pt \parindent 32pt \test }
When we set \type {\mathsurround} to \type {16pt} and \type {\parindent} to
\type {32pt} we get:
{\mathsurround 16pt \parindent 32pt \test }
We guess that the assumption is that a \type {\mathsurround} value different
from zero is not assumed when typesetting a paragraph or at least that the
assumption is that a paragraph does not start or finish with an inline math
formula.
This is what happens. A kern is added at the left and right side of a formula.
So we get: {\mathsurround32pt \boxsh\hbox{$xx$}}. When the paragraph is typeset,
this kern removed at linebreaks when needed.
% {\mathsurround32pt \dorecurse{20}{x {$xx$} xxx }}
However, as the start of a paragraph is no linebreak, it will stay there!
%{\mathsurround32pt \dorecurse{20}{$xx$ }} % overfulls
{\mathsurround32pt \dorecurse{20}{$xx$\hskip1em plus1em minus1em}\par}
If we use negative values we get similar effects:
{\mathsurround-32pt\boxsh\hbox{$xx$}}
Or in a vertical box:
{\mathsurround-32pt \dorecurse{20}{$xx$ } }
Maybe there is an opportunity here to implement marginal notes by abusing
a math formula at the start of a paragraph! After all, we've run into weirder
abuse of side effects.
\endinput